This invention relates generally to the control of burners, particularly gaseous fuel burners. More particularly, the invention relates to methods and apparatus for the control of such burners based on flame intensity.
Burners wherein a gaseous fuel such as natural gas, methane, propane, butane, ethane or the like, for example, is burned with a combustion oxidant gas such as oxygen, oxygen-enriched air or air, for example, are well known. For example, such gas burners find application in various residential, commercial and industrial combustion or heating assemblies such as those that include furnaces, water heaters, boilers, and the like.
In general, proper or desired operation of such burner apparatus involves responsive controlled operation beyond the mere supplying of fuel and oxidant at fixed flow rates. Unfortunately, such responsive control has to date proven relatively difficult and/or costly to achieve in a manner practical and economical for desired broader based applications.
It has long been recognized that flame intensity associated with the burning of such fuel and oxidant combustion mixtures is influenced by a variety of parameters, such as including firing rate, oxidant to fuel (also sometime referred to herein as "O/F" or, more specifically air to fuel ratio, when referring to systems wherein air is employed as the oxidant source), exact oxidant and fuel compositions, and the thermal environment of the flame, for example. It has also been long recognized that means to measure flame intensity are relatively simple and readily commercially available. In fact, flame intensity is routinely measured in many devices as a means of assuring the occurrence of combustion.
Numerous attempts have been made to apply simple flame intensity sensors to the control of oxidant to fuel ratio. Such a control method would significantly reduce the cost of oxidant to fuel ratio control, which is currently primarily achieved with rather expensive sensors that measure the concentration of oxygen in the exhaust. The simplicity and reduction in cost could open up considerable markets for oxidant to fuel ratio control for which it is currently unaffordable. In addition, since the measurement of flame intensity can be made at an individual burner, it would be possible to control the oxidant to fuel ratio from individual burners. In view thereof, potential applications include residential (e.g., air heating or water heating), commercial (e.g., air heating and boilers), industrial (e.g., furnaces and boilers), and power generation (e.g., boilers and gas turbines), for example. Thus, an invention that would enable such a control system could have considerable economic potential and impact.
Unfortunately, because of the dependency of flame intensity on parameters other than the oxidant to fuel ratio (such as parameters such as firing rate, fuel composition, and thermal environment, for example) it has been generally impossible to achieve oxidant to fuel ratio measurement with these sensors without knowing such other parameters as well.
It has also been recognized that the peak in the curve of flame intensity versus oxidant to fuel ratio generally occurs at the same oxidant to fuel ratio as long as the fuel composition is kept reasonably constant, for example, different compositions of natural gas are generally acceptable. Several measurement and control mechanisms based on this principle have been proposed. Unfortunately, the peak in the curve of flame intensity versus oxidant to fuel ratio typically or generally occurs at slightly or even significantly fuel rich conditions. For most combustion systems, operation under such fuel rich conditions is not desirable and for many combustion systems such operation is unacceptable. Consequently, various control schemes have been proposed that require only occasional operation at such fuel rich conditions, in order to calibrate the system. Unfortunately, application of such control schemes results in the control system not being a closed loop control system, but rather an open loop system with periodic calibrations. Furthermore, for some systems even periodic operation under such fuel rich conditions is unacceptable.
Thus, there is a need and a demand for a method and an apparatus for controlling such burner apparatus which more readily permits the use of relatively simple flame intensity sensors, such as known in the art.
In particular, there is a need and a demand for a relatively simple method and apparatus for the closed loop control of such burner apparatus. In addition, there is a need and a demand for burner apparatus control methods and apparatus which avoid or do not require undesired fuel rich condition operation.